SSD Soft Decoding Using Time-Temperature RBER Adjustment
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Solution Overview
Problem
Solid State Drive (SSD) devices, particularly those based on MLC and TLC technologies, face frequent soft decoding failures due to retention errors, leading to increased read operations and computational burdens, which result in latency and area overheads, as the number of bits per memory cell grows and threshold voltage distributions become closer, making it difficult to maintain acceptable Uncorrectable Bit Error Rates (UBER).
Innovation Solution
A method is introduced that adjusts the Raw Bit Error Rate (RBER) estimation based on SSD device parameters such as temperature and time since last programming, minimizing additional read operations by iteratively applying time and temperature indications to the reliability indication for soft decoding, and performing hard decoding when necessary to reduce errors and latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of bits per memory cell is increased (MLC/TLC technology), then storage capacity is improved, but threshold voltage distributions become closer and retention errors increase
Solution Approach 1:
The patent changes the parameter of RBER estimation by incorporating time since last programming and temperature indicators. Instead of using a fixed or simple RBER estimate, the system dynamically adjusts the RBER based on how long data has been stored and the operating temperature, which directly affects retention errors. This allows the soft decoding process to adapt to actual memory conditions, improving reliability while maintaining high storage capacity.
2Reliability
If additional read operations are performed to correct retention errors, then decoding reliability is improved, but latency and area overheads increase
Solution Approach 1:
The patent performs preliminary estimation of RBER using time and temperature indicators before actual decoding operations. By predicting the error rate in advance based on storage duration and temperature conditions, the system can prepare appropriate decoding parameters and confidence thresholds. This preliminary action avoids the need for multiple iterative read operations, reducing latency while maintaining decoding reliability.
3Measurement precision
If RBER estimation is made more accurate by considering time and temperature, then soft decoding performance is improved, but computational complexity increases
Solution Approach 1:
The patent introduces time since last programming and temperature as intermediary parameters that mediate between physical memory conditions and RBER estimation. These intermediaries simplify the complex relationship between storage conditions and error rates by providing measurable indicators that can be directly used to adjust RBER. This approach achieves accurate RBER estimation without requiring complex computational models, balancing precision and complexity.
Data Source
AI summary
A method is proposed for decoding read bits including information bits from memory cells of a solid state drive. The method comprises determining a reliability indication indicative of a reliability of the read bits, and iterating the following sequence of steps:soft decoding the read bits based on said reliability indication in order to obtain said information bits,determining at least one among a time indication indicative of a time elapsed since a last writing of the memory cells and a temperature indication indicative of a temperature of the memory cells, andapplying at least one among said time indication and said temperature indication to said reliability indication.A corresponding solid state drive is also proposed.